The present invention relates to an electrical connector assembly, and more particularly to a filter insert that is electrically coupled to the connector terminals for filtering electrical signals carried by the terminals.
Most electronic modules include a connector assembly for coupling the module to power supplies and external components such as sensors and actuators. Referring to FIG. 1A, a typical connector assembly 10 includes a matrix of terminals 12 supported in an insulator block 14 that passes through a wall of the module housing 16. The inboard ends of the terminals 12 are electrically coupled to a circuit board 18 enclosed by the module housing 16, while the outboard ends of the terminals 12 are accessible for electrical interconnection with a complementary connector and electrical cable (not shown). A filter insert 20 disposed between the insulator block 14 and the circuit board 18 is electrically coupled to the terminals 12, and includes filter elements such as capacitors for filtering electrical signals carried by the terminals 12. In many applications, such filtering is necessary in order to attenuate unwanted electrical noise as well as to reduce radiated electromagnetic emissions due to operation of the module. The insert 20 is provided with a matrix of openings 22 as seen in FIG. 1B, and is installed by aligning the openings 22 with the terminals 12, and pushing the insert 20 onto the terminal matrix. An encapsulating material 24 is injected into the region between the circuit board 18 and the insulator block 14 as shown in FIG. 1A for improved environmental sealing.
The filter insert 20 can be formed on a circuit board, on a rigid plastic substrate or on a flexible substrate. In cases where the insert is formed on a circuit board or a rigid plastic substrate, the terminals 12 can be soldered to metallic pads adjacent to the openings 22, or the openings 22 can be through-plated with metal so that a reliable electrical connection is established by virtue of an interference fit between the terminals 12 and the through-plated metal. An interference fit between the terminals 12 and the filter insert circuitry can also be achieved in cases where the insert 20 is formed on a flexible substrate by extending the circuit traces across the openings 22, leaving an opening that is smaller than the outline of a terminal 12. An example of a filter insert formed on a plastic substrate with through-plated openings is shown in the U.S. Pat. No. 6,413,119 to Gabrisko et al., while an example of a filter insert formed on a flexible substrate is disclosed in the U.S. Pat. No. 5,415,569 to Colleran et al.
Of the various filter insert designs discussed above, the flexible circuit approach is particularly attractive from a cost stand point, primarily because the interference fit electrical connections between the connector terminals 12 and the filter insert 20 permits low insertion force (compared to the through-plated approach) and eliminates the expense of soldering and/or through-plating. However, reliability testing has shown that when the module is subjected to extended thermal cycling, the thermal expansion and contraction of the encapsulating material 24 is transmitted to the flexible circuit, which in turn, leads to fatigue-related failures of the solder joints and traces formed on the circuit. Accordingly, what is needed is an improved filter insert having the low insertion force and low cost advantages of a flexible circuit, but with improved thermal cycle reliability.
The present invention is directed to an improved filter insert for a terminal connector, where the filter insert comprises a rigid substrate for good thermal cycle reliability and low-cost interference fit electrical connections between the filter insert and the connector terminals. In a first embodiment, the filter insert comprises a flexible circuit bonded to the rigid substrate, and the substrate is provided with over-sized openings that the terminals pass through without interference. A second embodiment is like the first, except that the filter circuit traces are formed directly on the rigid substrate, and the substrate material backing the terminal connection sites is removed to form the over-sized openings. The thermal bending stress applied to the traces and solder joints of the filter insert of this invention is considerably reduced compared to the flexible circuit approach, and the insertion force of the filter insert is essentially the same as with a flexible circuit due to the over-sized substrate openings.